With an increasing interest for access control plans and series of locking devices comprised therein, there is a market demand for easy to install locking devices that are operable both mechanically and electronically, without jeopardizing safety, both in terms of theft-prevention and automatically unlocking (fail-safe) in case of fire or other in-house threads.
FR 2,653,480 discloses a fail-safe locking device for emergency exits, the locking device comprising an electromagnet to maintain a latch in a closed position. When power supply to the electromagnet is interrupted, the latch is retracted in to the housing of the locking device by means of a spring. An electro-motor is provided for moving the latch to a closed position of the locking device after power supply is recovered.
A drawback of the locking device according to FR 2,653,480 is that it does not allow controlled opening and closing of the locking device without interrupting the current first and consecutively recovering power supply to the electromagnet and electro-motor.
A serious disadvantage of the locking device according to FR 2,653,480 is that in case power supply is interrupted while the electro-motor is moving the latch in a closed position, the fail-safe mechanism will fail to open the locking device for the reason that the electro-motor needs to be decoupled from a spindle actuating the latch first. As such it is clear that this locking device is not applicable for access control to access points that need to open and close on a regular basis.
WO 2008/094039 discloses a fail-safe locking device that will always open upon interruption of the power supply.
This locking device however has the drawback that it does not allow for a latch to be driven in a longitudinal direction of the housing and requires several holes to be provided in a door for placing the lock. Hence installation is cumbersome and the flexibility as to choose the position of the lock in a door is limited.
WO 87/04213, EP 0021670 and FR 2879643 disclose locking devices comprising drive means allowing moving a latch between a first position protruding from a frontal end of the lock housing and a second position wherein the latch is retracted in the housing; and further comprising a deactivation mechanism allowing movement of the drive means from an active position wherein the drive means are enabled to move the latch between the first and second position and a inactive position wherein the latch is retracted in the housing irrespective of its movement by the electrical drive means. The disclosed locking devices however have the disadvantage that the deactivation mechanism to be operated mechanically and will only be activated either manually or by activation of a alarming system. This may result in dangerous situations in case power supply is interrupted and no alarm is generated.
It is clear from the above that there remains a need for easy to install, versatile and reliable fail-safe locking devices.